The present invention generally relates to a nozzle and a method for dispensing process liquids onto a surface. More particularly, the present invention relates to a fluid dispense nozzle and method for dispensing developer chemicals onto a rotating semiconductor substrate material.
Integrated circuits are typically constructed by depositing a series of individual layers of predetermined materials on a wafer shaped semiconductor substrate, or "wafer". The individual layers of the integrated circuit are in turn produced by a series of manufacturing steps. For example, in forming an individual circuit layer on a wafer containing a previously formed circuit layer, an oxide, such as silicon dioxide, is deposited over the previously formed circuit layer to provide an insulating layer for the circuit. A pattern for the next circuit layer is then formed on the wafer using a radiation alterable material, known as photoresist.
Photoresist materials are generally composed of a mixture of organic resins, sensitizers and solvents. Sensitizers are compounds, such as diazonaphthaquinones, that undergo a chemical change upon exposure to radiant energy, such as visible and ultraviolet light resulting in an irradiated material having differing salvation characteristics with respect to various solvents than the nonirradiated material. Resins are used to provide mechanical strength to the photoresist and the solvents serve to lower the viscosity of the photoresist so that it can be uniformly applied to the surface of the wafers.
After a photoresist layer is applied to the wafer surface, the solvents are evaporated and the photoresist layer is hardened, usually by heat treating the wafer. The photoresist layer is then selectively irradiated by placing a radiation opaque mask containing a transparent portion defining the pattern for the next circuit layer over the photoresist layer and then exposing the photoresist layer to radiation. The photoresist layer is then exposed to a chemical, known as developer, in which either the irradiated or the nonirradiated photoresist is soluble and the photoresist is removed in the pattern defined by the mask, selectively exposing portions of the underlying insulating layer.
The exposed portions of the insulating layer are then selectively removed using an etchant to expose corresponding sections of the underlying circuit layer. The photoresist must be resistant to the etchant, so as to limit the attack of the etchant to only the exposed portions of the insulating layer.
Alternatively, the exposed underlying layer(s) may be implanted with ions which do not penetrate the photoresist layer thereby selectively penetrating only those portions of the underlying layer not covered by the photoresist. The remaining photoresist is then stripped using either a solvent, or a strong oxidizer in the form of a liquid or a gas in the plasma state. The next layer is then deposited and the process is repeated until fabrication of the semiconductor device is complete.
Developer solution and other process liquids are typically applied to the wafer using a spin coating technique in which the process liquid is sprayed on the surface of the wafer as the wafer is spun on a rotating chuck. The spinning of the wafer distributes the liquid over the surface of the material. When developer chemicals are applied to the surface, it is necessary to quickly and gently produce a deep puddle of developer on the wafer to ensure that the photoresist layer is dissolved uniformly in areas that are soluble in the developer.
A common practice in the prior art is to spray the process liquid onto the surface of the wafer from a source positioned high enough above the wafer to ensure that the spray fully covers the wafer. However, the process liquid develops a significant amount of momentum prior to contacting the surface that greatly disturbs the surface of photoresist material. Although the surface of the wafer is very smooth, the impact of the process liquid being dispensed onto the wafer results in a nonuniform distribution of the process liquid. In the case of applying developer solution, the turbulence caused by the impact of the developer increases the possibility that air bubbles will form in the developer and that uneven salvation of the photoresist will occur due to agitation caused by local mixing. Both of these problems decrease the uniformity and contribute to defects which reduce the overall yield of properly performing chips from the wafer.
Several attempts have been made in the prior art to minimize the aforementioned problems, such as disclosed in U.S. Pat. No. 5,002,008 issued to Ushijima et al., U.S. Pat. No. 5,020,200 issued to Mimasaka et al. and U.S. Pat. No. 5,429,912 issued to Neoh. The Ushijima patent discloses a nozzle having a trumpet shaped tip to prevent inadvertent dripping of the process material onto the wafer and threaded to the dispense arm to minimize the leakage of air into the nozzle itself. The nozzle is positioned in close proximity to the wafer and dispenses the process material perpendicular to the surface. The process material is distributed over the surface of the wafer by the spinning motion of the wafer on the chuck.
The Neoh patent discloses a nozzle apparatus that contains a well immediately upstream of the dispense end of the nozzle. The well provides a large flow area that slows the flow of the process material, allowing air pockets that may have been formed during the pumping of the material to the well to separate from the process material as a result of buoyancy and be removed from the nozzle. As with the Ushijima patent, the nozzle is positioned in close proximity to the wafer and dispenses the process material perpendicular to the surface. The process material is distributed over the surface of the wafer by the spinning motion of the wafer on the chuck. While the Ushijima and Neoh patents disclose nozzles that provide the aforementioned improvements, the process material is dispensed perpendicular to the surface in a small area proximate to the nozzle, which can cause nonuniformities in the surface of the coating layer due to the impact of the material as discussed previously.
The Mimasaka patent discloses a cylindrically shaped nozzle that contains a plurality of holes through the side of the nozzle in a direction parallel to the surface of the wafer. The nozzle produces a lower impact velocity of the process material by forcing the flow, which initially is perpendicular to the surface of the wafer to turn 180.degree. after encountering blockage at the bottom of the nozzle and to exit the nozzle through holes in the side of the nozzle. The impact velocity of the process material is substantially lowered because the fluid has lost almost all of its momentum perpendicular to the wafer when it encountered the blockage in the nozzle; therefore only the gravitational acceleration of the fluid over the short distance from the holes in the nozzle to the surface of the wafer will contribute to the perpendicular component of the impact velocity.
Certain difficulties exist with the use of the Mimasaka nozzle. For instance, because the flow does not exit from the bottom of the nozzle, the nozzle must be positioned off the centerline of the wafer so that the flow exiting the holes contacts the center of the spinning wafer. The off-centerline positioning of the nozzle is not necessarily a less favorable orientation; however, the placement of the Mimasaka nozzle requires far more precision than the bottom dispense nozzles of the prior art. Both the bottom dispense and the Mimasaka nozzles have to be radially positioned over the centerline of the wafer to ensure full coverage requiring accuracy in the positioning of the nozzle on a scale of the liquid stream dimensions. The Mimasaka nozzle, however, must additionally be angularly positioned so that one hole on the circumference of the nozzle is aligned with the centerline of the wafer, while maintaining the proper radial alignment. The additional complexity of the alignment procedure was apparently recognized in the Mimasaka patent as an alternative embodiment also provides holes in the bottom of the nozzle. This embodiment, however, is fraught with the same problems as other prior art designs in which the fluid exits perpendicular to the surface of the wafer. Also, the use of a plurality of holes increases the potential for the liquid to drip onto the surface of the wafer after dispensing is completed, because the holes can act as vents and drains for the flow that facilitates the formation of drops.
In addition, because the flow generally must turn 180.degree. and must exit through flow holes the flow path is necessarily extremely tortuous. In fact, the tortuous path is the means by which the Mimasaka nozzle lowers the impact velocity of the process material. The tortuosity of the flow path produces turbulence in the flow, even at low Reynolds numbers, which greatly increases the possibility that air will get trapped in the process material and that chaotic motion of the flow will disrupt the coating layer.
Thus, it is apparent that a need exists for an improved nozzle for spin dispensing apparatuses which overcomes, among others, the above-discussed problems so as to produce a more uniform layer of process liquid over the surface of the wafer.